Researchers at the University of California San Diego have developed a new computational approach to accurately model and predict complex spin structures called helimagnetic spin structures, using quantum mechanics calculations.
“The helical spin structures in two-dimensional layered materials have been experimentally observed for over 40 years. It has been a longstanding challenge to predict them with precision,” said Kesong Yang, professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering and senior author of the study. “The helical period in the layered compound extends up to 48 nanometers, making it extremely difficult to accurately calculate all the electron and spin interactions at this scale.”
In this novel approach, researchers calculated how the total energy of a chiral helimagnet changes as the spin rotation shifts between successive layers of atoms. By applying first-principles quantum mechanics calculations, they were able to map out the critical features of these spiraling structures. “Rather than modeling the entire system at a large length scale, we chose to focus on how spin rotation affects the total energy of the system,” said study first author Yun Chen, a nanoengineering Ph.D. student in Yang’s group. “By using a small supercell and designing optimized spin configurations, we were able to obtain highly accurate results.”
The scientists tested their approach on a group of chiral helimagnets containing chromium, a metal known for its magnetic properties. The team successfully predicted three key parameters: the helix wavevector, which describes how tightly the spins spiral; the helix period, or the length of one complete spiral turn; and the critical magnetic field, the strength of an external field needed to alter the helimagnet’s structure.
“This is exciting because we can now precisely model these complex spin structures using quantum mechanics calculations, opening new opportunities for designing better materials,” said Yang.